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Page:Popular Science Monthly Volume 54.djvu/487

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transported by temporary and permanent currents thousands of miles away, where it is deposited in the more quiet waters of the ocean. In this manner the Mississippi has been shown to deposit a cubic mile of mechanically transported material in a little over a century. What shall we say of the effects produced on the continents and oceans by thousands of rivers, each doing its proportionate share of work and acting through millions of years? Two main results must follow, unless interruptions occur: the lower elevations and the magnificent mountain ranges, which rear their lofty heads above the permanent snow line, will be divided into minor peaks; valleys will be carved

PSM V54 D487 The mississippi delta.png
Fig. 6.—The Delta of the Mississippi.

out; the whole land surface will slowly waste away, at first rapidly, at last slowly, and be transported to the oceans, where it will form great horizontal beds differing in no essential particular, excepting size, from those shown in Fig. 5—great deposits that are merely deltas on a large scale. The geologist, however, finds no evidence to indicate that at any time in the earth's history have these theoretical results taken place. Land masses, of continental dimensions, have not been allowed thus to waste entirely away to a general flatness on account of the interruptions caused by elevation—the bodily lifting of great areas of rock, even out of the ocean floor, to become mountains or plateaus, in some cases higher than any point in this country. If our observations thus far and those yet to be made serve to make this clear, one of the objects of this article will have been